Researchers Discover Second Native Hawaiian Bat

The Hawaiian Islands have long been thought to support just one endemic land mammal, the Hawaiian hoary bat. But new fossil evidence indicates that a second, very different species of bat lived alongside the hoary bat for thousands of years before going extinct shortly after humans arrived on the islands.

Skeleton of Synemporion keana embedded in the wall of of Māhiehie Cave on Maui.

The research, published this week in the journal American Museum Novitates, describes the mysterious bat, named Synemporion keana, whose remains were first discovered in a lava tube more than 30 years ago.

“Besides the animals that humans have introduced to the islands, like rats and pigs, the only mammals that we’ve known to be native to Hawaii are a monk seal, which is primarily aquatic, and the hoary bat,” said Nancy Simmons, a co-author on the paper and curator-in-charge of the American Museum of Natural History’s Department of Mammalogy. “So finding that there actually was a different bat—a second native land mammal for the islands—living there for such a long period of time was quite a surprise.”

Synemporion keana first appeared in the fossil record on the islands around 320,000 years ago and survived until at least 1,100 years ago, coexisting alongside the hoary bat for several thousand years. It is known that Synemporion keana was a vesper, or evening bat, but its array of features means that identifying its closest relatives has been challenging. Simmons and her colleagues hope that future work with ancient DNA extracted from the fossils might help them solve the mystery.

“This extinct bat really is something new, not just a slight variation on a theme of a known genus,” Simmons said. “The new bat contains a mosaic of features from taxa seen on many different continents.”

The skull of the holotype of Synemporion keana (A), compared with the Hawaiian hoary bat (B).

The authors think that the extinction of Synemporion keana may have been a direct or indirect result of human colonization of the islands and the invasive non-native species that accompanied human explorers and settlers.

“It seems possible that the reduction of native forests and associated insects after human colonization of the islands contributed not just to the extinction of plants, birds, and invertebrates, but also to the extinction of this endemic bat,” said Francis Howarth, an entomologist at the Bishop Museum in Honolulu and co-author on the paper.